''Adelalopus'' is an extinct genus of palaelodid bird from the lowermost

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

. It is the oldest member of its family and the largest known palaelodid from Europe, slightly larger than '' Megapaloelodus goliath''. It contains a single species, ''Adelalopus hoogbutseliensis''.

History and naming

The remains of ''Adelalopus'' were discovered at the locality of Hoogbutsel,

, approximately east of

Brussels Brussels, officially the Brussels-Capital Region, (All text and all but one graphic show the English name as Brussels-Capital Region.) is a Communities, regions and language areas of Belgium#Regions, region of Belgium comprising #Municipalit ...

and are stored at the Museum of Natural Sciences of Belgium. The type specimen IRScNB Av 71 consists of an incomplete

furcula The (Latin for "little fork"; : furculae) or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is either an interclavicle or formed by the fusion of the two clavicles. In birds, its primary function is ...

, parts of a

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

, a

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

, the distal end of an

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

and the shaft of a

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

as well as an incomplete

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) a ...

. A second specimen (IRScNB Av 72) is referred to the genus, consisting of the extremitas omalis of the left coracoid. The same element is present for the right coracoid in the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

. All material included in the type specimen is considered to be from a single individual based on the proximity of the bones, their size and their similar surface texture. The referred coracoid was found in a different box, but may potentially have belonged to the same individual as well. The name ''Adelalopus'' is an

anagram An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word ''anagram'' itself can be rearranged into the phrase "nag a ram"; which ...

of ''

Palaelodus ''Palaelodus'' is an extinct genus of bird of the Palaelodidae family, distantly related to flamingos. They were slender birds with long, thin legs and a long neck resembling their modern relatives, but likely lived very different livestyles. The ...

'', a relative of the genus. The species name references the type locality.

Description

The

has a wide U-shape and on the caudal surface of the extremitas sternalis there is a marked depression like in ''Palaelodus''. Unlike in ''Palaeolodus'' however the center of this element contains a deep and elongated cavity, which is regarded as one of the genus' diagnostic features. The apophysis of the wishbone is larger and better developed than in modern flamingos but incomplete. The

is similar to that of ''

Megapaloelodus ''Megapaloelodus'' is an extinct genus of stem flamingo of the family Palaelodidae. ''Megapaloelodus'' is primarily known from Miocene America, from South Dakota and Oregon in the north to Argentina in the south, but the species ''Megapaloelodus g ...

'', with the facies that articulates with the

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

overhanging two pits separated from each other by a bulge. These same bits are weak in ''Palaelodus'' and missing entirely in modern flamingos. The medial and lateral sides of the cotyla scapularis are not sharply differentiated and the foramen for the supracoracoid nerve is well-developed and elliptical like in basal-anseriforms and phoenicopteriforms. The

is short with a slender shaft similar to ''Palaeolodus''. The incomplete nature of the

makes comparison difficult, but it generally resembles what is expected from palaelodids and modern flamingos. Although fragmentary, the

is diagnostic. Its cross section is rectangular like in modern flamingos and not compressed like in other palaelodids. The distal vascular foramen is larger and longer than in either palaelodids or phoenicopterids and in this state more closely resembles the Eocene bird ''

Juncitarsus ''Juncitarsus'' is an extinct genus of wading birds from the Eocene of the United States and Germany. Though previously considered a flamingo, it is likely outside of Phoenicopteridae, possibly a basal member of the Mirandornithes (neither Phoeni ...

'', which has been recovered as either a basal member of

Mirandornithes Mirandornithes () is a clade that consists of flamingos and grebes. Many scholars use the term Phoenicopterimorphae for the superorder containing flamingoes and grebes. Determining the relationships of both groups has been problematic. Flaming ...

or a stem-Phoenicopteriform. The trochlea of the second digit faces plantar like typical for the group and was positioned higher than the trochlea of the following two toes. As seen in ''Palaelodus'', this trochlea was located further up than in modern flamingos. ''Adelalopus'' is slightly larger than '' Megapaloelodus goliath'', making it one of the largest members of the Palaelodidae. The individual bones are identical in size to the extant

coscoroba swan The coscoroba swan (''Coscoroba coscoroba'') is a species of waterfowl in the subfamily Anserinae of the family Anatidae.HBW and BirdLife International (2021) Handbook of the Birds of the World and BirdLife International digital checklist of the ...

from South America.

Paleoecology

The Hoogbutsel locality where the remains of ''Adelalopus'' were found is thought to represent what was once the shore of a lagoon. With the locality being considered to be early Oligocene in age, ''Adelalopus'' would be among the earliest known palaelodids. The function of the deep cavity located on the furcula is not known, it is however thought to be too large to be a simple pneumatic foramen and too small to enclose a tracheal loop.

References

{{Taxonbar, from=Q90123043 Phoenicopteriformes Fossil taxa described in 2002 Fossils of Belgium